Numerous apparatus and methods for use in detecting and/or quantifying the presence of analytes in a sample have been developed. Such tests can be used, for example, to define the exact composition of a sample (qualitative assay) or to determine the precise amount or concentration of any given analyte in that sample (quantitative assay). Practical applications of such tests include environmental monitoring, medical research and analysis.
Common methods in the field of medical research and analysis include polypeptide and polynucleotide assays.
Examples of polypeptide assays include immunoassays, ELISA and Western blotting, all of which are based on the principle of antibody/antigen interaction. Immunoassays, for example, are usually carried out in multi-well plates. However, using such apparatus means that only a single analyte can be tested in each well. Assays for testing large numbers of compounds simultaneously have been developed. However, to date, these have mostly been limited to polynucleotide assays.
Polynucleotide assays, which are based on hybridisation between complementary nucleic acid sequences, include Northern and Southern blots, PCR and, more recently, micro-arrays. While micro-arrays allow up to several thousand compounds to be tested simultaneously, they have the disadvantage of generally requiring all analytes to be tested against a single sample.
Current polypeptide and polynucleotide assays are therefore restrictive in terms of the actual number of individual binding assays that can be performed at any one time. In addition, current methods are often not capable of detecting small amounts of a test substance. The most recognised explanation for this is the problem of background staining whereby irrelevant analytes bind non-specifically and particulate matter prevents analyte-specific binding and, after completion of an assay, often remains on the test surface thereby interfering with specific signalling and the clarity and reliability of any readouts.
There is therefore a need to develop improved methods for performing such assays. The present invention seeks to overcome at least some of the aforementioned problems, and seeks to provide an assay method, and apparatus for use therein, which is precise, reproducible, accurate, sensitive and specific.